Influence of Fe Source On Marigold Nutrition, Substrate Chemistry, and Nutrient Runoff: Cu, Fe, Mn, and Zn

Fertilizers used in the production of greenhouse crops usually contain Fe chelates.  There is considerable information on the effects of Fe-chelates on Fe nutrition; there is less information available, however, on the effects of Fe chelates on other micronutrient metals in plant nutrition, substrate solution, and leachate runoff.  Therefore the objectives of the study were to determine the effects of Fe source on these factors during the production cycle of marigold.  Iron source treatments consisted of iron sulfate (FeSO₄), iron ethylenediaminetetraacetic acid (FeEDTA), iron ethylenediaminedisuccinic acid (FeEDDS), iron diethylenetriaminepentaacetic acid (FeDTPA), and iron ethylenediamine-N,N'-bis(2-hydroxyphenylacetic) acid (FeEDDHA) added to a base nutrient solution at the rate of 1 mg•L^-1 Fe final concentration.  Treatments were applied to marigold (Tagetes erecta, ‘First Lady’) growing in peat-based media in six-celled grow-packs.  Iron treatment was not significant for foliar Fe, Mn, or Zn, averaging 165 μg•g^-1 Fe, 228 μg•g^-1 Mn, and 35 μg•g^-1 Zn.  Iron treatment was significant for foliar Cu with FeEDDHA, FeDTPA and FeEDDS having a mean value of 6.85 μg•g^-1 vs. 4.58 μg•g^-1 in the FeSO4 treatment.  Substrate analysis by pour-through technique over the course of the study revealed that the FeDTPA treatment had the highest levels of Cu (by 82%), Fe (by 69%), Mn (by 14%), and Zn (by 66%) in substrate solution extract.  Leachate runoff was collected over the course of the study with the FeDTPA treatment had the highest levels of Cu (by 33%), Fe (by 61%), and Zn (by 25%); while Mn was highest in the FeEDTA treatment by 16% in runoff.